You either have an electrical short to the gauge or your temperature sensor on the motor is "out to lunch". Try to manually get your motor temperature with some other sort of thermometer. With a cold engine take the radiator cap off and make sure it is full. Then place a thermometer in being sure to touch the fluid(may sound dumb but don't drop it in the radiator). Start the engine and allow it to come up to operating temperature. Approximately 190 to 200 degrees. Your thermostat should be open at this point and you should notice a flow to the radiator fluid. If the temp holds then you have one of the aforementioned problems. If you have a Haynes manual it should tell you how to troubleshoot the temperature sensor. I believe that I am leaning towards an electrical short of some sort though. An improper ground perhaps. Check and see if there are any fuses that control this system. Once again, the Haynes manual has wiring diagrams that will show you what wires to chase. And it is a chase. wiring problems are hard to find. If the temperature test pans out You may want to buy an after market temperature gauge and mount it up instead. Pull the plug on the old one and be on the road. You may have already solved this problem and I just wasted about five minutes of my life. If not and you have any questions e-mail me at [email protected]
Have fun and be careful. 200 degree fluid is nothing to take lightly.